Badger cull: Time for a Christmas ceasefire?

England has a new festive tradition. In the season of mince pies, office parties, and panto, comes the annual announcement of badger slaughter. This year was no different – on the afternoon of December 21, when many people had left for the Christmas break and the parliamentary recess was just a few hours away, the government quietly announced that 19,274 badgers had been killed across 17 areas in seven weeks, with two cull areas still to announce their totals.

To give that number some meaning, 19,274 badgers would weigh about the same as two and a half space shuttles. If you laid all those badgers nose to tail, it would take you three hours to walk from one end of the line to the other. The cull is likely to have cost taxpayers in the region of £10 million. Slaughter on this scale had better be worth it.

The culls are a desperate attempt to halt the spread of bovine tuberculosis (TB), a cattle disease which can be devastating for farming businesses and farming families. TB is a serious problem and it needs a serious solution. But there is little evidence that badger culling offers such a solution.

Eustice referred to this year’s culls as "effective", which would seem to imply that they are already working to reduce cattle TB. In fact it means no such thing (it takes nearly two years to accumulate and analyse the data on how each cull affects cattle TB, so the outcomes of this year’s culls won’t be known until 2019).

In government-speak, an “effective” cull means one which reduces badger numbers by at least 70% and so might be expected to reduce cattle TB if repeated annually for four years. Unfortunately, no one has any idea whether the 2017 culls reduced badger numbers by “at least 70%”. All the culls were given target numbers of badgers to kill, but these are based on shockingly bad science: in each cull zone, initial targets are set without any on-the ground surveying of the badger population, and all targets are set deliberately low to make them more achievable. In 10 of the 11 new areas culled in 2017, targets were further lowered in the course of culling, and the method used to update these targets drew on eight previous “effective” culls, of which five had also had their targets lowered in the course of culling. This intricate number-mangling would be funny if the numbers didn’t describe something so serious.

The authors’ statement of caution is both important and justified, because the paper’s findings are not robust. The paper describes cattle TB incidence in the first two culling areas for the first two years of culling – a tiny sample size. A relatively simple primary analysis found no significant difference in cattle TB incidence between culled and unculled comparison areas. Significant differences emerged only when eight other variables were included in the analyses.

According to these more complex analyses, one of the two areas had had lower cattle TB than its comparison areas before culling started, making it hard to be confident that any differences were caused by culling. For the second area, cattle TB appeared lower inside the cull zone and higher on adjoining land, relative to comparison areas, but these differences collapsed when one of the 10 comparison areas, or one of the eight covariates, was excluded from the analysis.

Such statistically fragile results are common when datasets are small, and would not usually be published when more data were accumulating. The government has not published similar analyses for a third year of data, when the then-newest cull zone saw its annual number of newly-affected herds rise from an average of 27 herds per year for the three years before culling started, to 35 after the first year of culling. Despite the government’s claims of success, and the desperate hopes of thousands of farmers in TB-affected England, it is too early to say whether the badger culls are working.

In its desperation to claim success, the government has sacrificed evidence-based policymaking. Badger culls are claimed to be “effective” before the impacts on cattle can be measured, and however few badgers they have killed. Culling is described as “driving down levels of TB” even when the scientists analysing cattle TB warn that no such inference should be made. By hyping the evidence in this way, the government does a disservice to farmers, who need to make investment decisions about tackling TB based on facts not fudge. They also do a disservice to the taxpayers who generally do not support the culls but are nevertheless paying for them. Finally, they do a disservice to badgers themselves, and the millions of people who feel that England’s countryside is enriched by these ancient inhabitants.

ZSL Institute of Zoology researchers are embarking on an exciting fieldwork expedition to Nelson’s Island in the Chagos Archipelago. Throughout the month, the team will share their research and experiences on an uninhabited tropical island!